Why stock parts are sometimes needed in project cars

If you've watched the episodes where MOOG discovers the ECU is fried (CLICK HERE) and then when Marty and VAG Commander Myles fix it in secret (CLICK HERE) through a long process of electronic shenanigans.

A lot of followers asked why we didn't just rip the stock ECU out and bash a Haltech in to get the car running straight away. Well, the answer isn't that simple and getting the Up! GTI swap to run and function as a car almost involved more work on laptops than physical spanner-twirling and bolt-threading.   

Long-time followers of the show know we have had a fantastic, ongoing relationship with the legends at Haltech for over a decade, but the answer to fixing the Up! wasn't as simple as jamming an aftermarket ECU into it and hitting PgUp until it pinged a rod into a low orbit. 

Unlike our beloved classic nuggets, modern cars feature incredibly complex wiring systems integrating functions that means replacing an ECU can affect headlights, your air-conditioning, power steering, and windscreen wipers.

While a Haltech R5 Nexus and PD16 PDM can run all these functions (and they have on a bunch of our project cars!), the direct-injection systems used by modern Volkswagen-Audi Group (VAG) cars isn't able to be controlled yet. 

Direct injection (or DI) is where fuel is squirted directly into the combustion chamber at extremely high-pressures. This is done so manufacturers have far more control over each injection of fuel, and it happens at insanely fast rates. Basically, it is incredibly complex.

Traditional port injection is where injectors spray fuel from above the intake port, and most cars with this style of electronic fuel-injection will still cop Haltech ECUs and VCUs from us as they're the best way to control those engines.

We could use stock ECUs on those cars and remap or flash-tune them, but the less intuitive tuning interface and programming limitations (what the stock ECUs can do versus a full standalone ECU/VCU) mean Haltech will get our projects working quicker and easier. 

Back to fixing the Up! GTI, and this project taught us just how involved the wiring and ECUs of modern European cars are, as they literally control every function of the vehicle. In days gone by people did these types of vehicle swaps by putting everything from the donor car into the new shell as a way of trying to trick the computer, but the integrated electronnic functions of modern VAG cars means it is no longer that simple. 

Body control modules have long been used by manufacturers (even back to the 1990s) to provide security. They wanted to make it impossible to steal a car by bringing your own key, ignition barrel and ECU, plugging those parts in and driving away... which actually used to happen with some early EFI cars. 

However people wanting to put late-model EFI hardware into cars that didn't have that stuff discovered these body control modules needed to be turned off via programming or by tricking the ECU, so the computer didn't go looking for them. This is where an aftermarket ECU made engine-swapping infinitely easier as they don't rely on body control modules.

Thankfully, we have a VAG Commander in our midst and Myles was able to unlock the electronics and get the Up! GTI working how it should with all its functions like headlights, air-conditioning, and wipers.